202 JACQUES LOEB 



2. Our analysis of the process of the causation of development 

 has led us to the result that it requires generally the cooperation 

 of two factors (or substances) ; one which calls forth the membrane 

 formation (or the change in the cortical layer of the egg); and 

 a second factor which saves the egg from the disintegration with 

 which it is usually threatened after membrane formation. This 

 second — corrective — factor is most conveniently supplied in the 

 form of a short treatment of the egg with a hypertonic solution.^ 

 The question therefore presented itself to which of these two fac- 

 tors the life-saving effect of the act of fertilization was due. 



The natural inference from our former experiences would have 

 been to ascribe the life-saving effect of the act of fertilization to 

 the second corrective factor for the following reason. If we 

 cause artificial membrane formation in the unfertilized egg of the 

 sea urchin, we do not prolong its- life but on the contrary we 

 shorten it. Such an egg dies at room temperature in a few hours 

 while without the membrane formation it may live at least for 

 a few days. The artificial membrane formation alone (if it is 

 not followed by the second corrective factor) hastens the death 

 of the unfertilized egg. We can understand the reason for this 

 since the artificial membrane formation accelerates the rate of 

 oxidations in the sea urchin egg to exactly the same amount as the 

 entrance of a spermatozoon (Warburg/ Loeb and Wasteneys^). 

 By the way of exclusion this seemed to restrict the life-saving 

 effect of the act of fertilization as well as of artificial partheno- 

 genesis to the second corrective factor. 



3. Observations which the writer made this winter, however, 

 show that this conclusion is not correct. In his earlier work he 

 had already found that the hypertonic solution is just as effective 

 as a corrective factor if it precedes the artificial membrane forma- 

 tion as if it follows it. The only difference between the two 

 cases is a difference in the time of exposure required. When the 

 artificial membrane formation is called forth first and the eggs 

 are exposed to the hypertonic solution (50 cc. sea water -\- 8 cc. 



' Loeb, Die chemische Entwicklungserregung des tierischen Eies, Berlin, 1909. 

 The mechanistic conception of life, 1912. 



* Warburg, Zeitschr. physiol. Chemie, vol. 66, p. 305, 1910. 



* Loeb and Wasteneys, Journ. Biol. Chemistry, vol. 14, p. 469, 1913. 



